1. Field of the Invention
The present invention relates to an absorbent composition comprising each of an acidic and a basic material, wherein the absorbent composition exhibits desirable absorbent properties. Specifically, the present invention relates to an absorbent composition having the ability to slowly absorb a large quantity of liquid, particularly while under an external pressure. The absorbent composition is useful in disposable absorbent products, such as those disposable absorbent products that are used to absorb bodily liquids.
2. Description of the Related Art
The use of water-swellable, generally water-insoluble absorbent materials, commonly known as superabsorbents, in disposable absorbent personal care products is known. Such absorbent materials are generally employed in absorbent products such as diapers, training pants, adult incontinence products, and feminine care products in order to increase the absorbent capacity of such products while reducing their overall bulk. Such absorbent materials are generally present in absorbent products in a fibrous matrix, such as a matrix of wood pulp fluff. A matrix of wood pulp fluff generally has an absorbent capacity of about 6 grams of liquid per gram of fluff. The superabsorbent materials generally have an absorbent capacity of at least about 10, preferably of about 20, and often of up to 100 times their weight in water. Clearly, incorporation of such absorbent materials in personal care products can reduce the overall bulk while increasing the absorbent capacity of such products.
A wide variety of materials has been described for use as absorbent materials in personal care products. Such materials include natural-based materials such as agar, pectin, gums, carboxyalkyl starch, and carboxyalkyl cellulose, as well as synthetic materials such as polyacrylates, polyacrylamides, and hydrolyzed polyacrylonitrile. While such natural-based absorbent materials are known for use in personal care products, they have not gained wide usage in such products. The natural-based absorbent materials have not gained wide usage in personal care products, at least in part, because their absorbent properties are generally inferior compared to the synthetic absorbent materials, such as the sodium polyacrylates. Specifically, many of the natural-based materials tend to form soft, gelatinous masses when swollen with a liquid. When employed in absorbent products, the presence of such soft gelatinous masses tends to prevent the transport of liquid within the fibrous matrix in which the absorbent materials are incorporated. This phenomenon is known as gel-blocking. Once gel-blocking occurs, subsequent insults of liquid cannot be efficiently absorbed by the product, and the product tends to leak. Further, many of the natural-based materials exhibit poor absorption properties, particularly when subjected to external pressures.
In contrast, the synthetic absorbent materials are often capable of absorbing large quantities of liquid while maintaining a generally stiff, non-mucilaginous character. Accordingly, the synthetic absorbent materials can be incorporated in absorbent products while minimizing the likelihood of gel-blocking.
One property of currently available superabsorbent materials is that such materials typically very rapidly absorb the liquid that comes into contact with the superabsorbent material. While such quick absorbency of the liquid may be desirable in many applications, there are certain applications in which it is not desirable. For example, in an absorbent structure that is insulted with a liquid at only a very localized location, it would generally be desirable to have the liquid distributed throughout the entire volume of the absorbent structure so that the absorbent capacity of the entire absorbent structure is utilized. However, if the superabsorbent material located near the localized insult location absorbs the liquid very quickly, such superabsorbent material may swell and block the flow of the liquid throughout the rest of the absorbent structure, possibly resulting in the liquid leaking out of the absorbent structure in the area of the localized insult location. As such, it may be desirable to employ a superabsorbent material in the localized insult location that actually absorbs the liquid at a slow rate. This would allow the liquid to be distributed throughout the absorbent structure first and then be subsequently absorbed by the slowly-absorbing superabsorbent material.
Several methods are known to slow down the liquid absorbing rate of a relatively fast-rate-absorbing superabsorbent material. For example, it is possible to coat the fast-rate-absorbing superabsorbent material with a material that is nonabsorbent and/or hydrophobic. Such coating materials tend to temporarily shield the underlying superabsorbent material from any liquid and, thus, delay the absorption of the liquid by the superabsorbent material. However, such coating materials often reduce the overall liquid capacity of the superabsorbent material, add to the expense and complexity of preparing the superabsorbent material, and may negatively affect other liquid handling properties of the superabsorbent material.
It is, therefore, an object of the present invention to provide an absorbent composition that absorbs a liquid at a relatively slower rate but with about the same final capacity as compared to commercially available synthetic, superabsorbent materials.
It is also an object of the present invention to provide an absorbent composition that may be prepared from natural-based materials since such may reduce the overall cost of preparing the absorbent composition as well as providing for additional beneficial properties of the absorbent composition such as biodegradability or compostability.
It is also an object of the present invention to provide an absorbent composition that may be prepared simply and with a minimum of materials and additives so as to reduce the overall cost of preparing the absorbent composition as well as reduce the potential deleterious effect that such additives might have on the overall absorbent properties of the absorbent composition.
It is also an object of the present invention to provide an absorbent composition that exhibits unique properties so that such absorbent composition may be used in novel applications.